The present invention is generally directed to a control point driver circuit and is particularly directed to a control point driver circuit for use in a telephone exchange for energizing and de-energizing a control relay in response to set and reset input pulses.
Control point driver circuits are well known in the art and find general application in telephone exchanges for energizing and de-energizing control relays. Reference to such circuits is found in an article by Edward M. Horiuchi and Otto J. Kohout, "#2 EAX Techniques," GTE Automatic Electric Technical Journal, volume 15 no. 3, July, 1976, pages 156-158. It is advantageous for such control point driver circuits to be bi-stable in nature so that a continuous input pulse is not required for holding a control element such as a control relay energized or de-energized. Unfortunately, such control point driver circuits suffer from being sensitive to supply line noise which gives rise to inadvertant energizing or de-energizing of the control relays or are quite complicated requiring a substantial number of discrete components. Control point driver circuits of the prior art have also lacked repeatability and stability in the triggering threshold levels. Also, control point driver circuits of the prior art have lacked sufficient electrical isolation between the set and reset control pulses and the control point itself. This is important because this factor adds substantially to its noise immunity, particularly where large ground-potential differences exist between the control point driver circuit and the circuits which supply the control set and reset pulses. Additionally, such control point driver circuits do not facilitate the required degree of decoupling in order to afford reliable service.
It is therefore a general object of the present invention to provide a new and improved control point driver circuit for use in a telephone exchange.
It is a more particular object of the present invention to provide a control point driver circuit which is substantially less complicated than control point driver circuits which have come before.
It is a still further particular object of the present invention to provide a control point driver circuit for use in a telephone exchange for energizing and de-energizing a control relay which substantially precludes noise from affecting its operation.
It is a still more further particular object of the present invention to provide a new and imporved control point driver circuit which affords improved repeatability and stability of the triggering threshold level.